A close up view of a Black-Eyed Susan cultivar.
Black-Eyed Susan Cultivar
by Brian Johnston (Canada)
This member of the Asteraceae
a cultivar of the North American wildflower commonly called the
‘Black-Eyed Susan’, ‘Gloriosa Daisy’ or ‘Yellow Oxeye
Rudbeckia hirta ‘Indian
Summer’ produces large 6 to 9 inch diameter
flower-heads with orange–yellow ray flowers and purplish-brown
centres. Large flower cultivars are usually produced by
‘normal’ plants with DNA altering radiation, or DNA altering
such as colchicine.
The genus name Rudbeckia was chosen
in the 18th century by the developer of modern
Linneaus, to honour one of his botany teachers, Professor Olof
the Younger, and his teacher’s father, Olof Rudbeck the Elder.
The buds of this Black-Eyed
are not particularly colourful, but they are unusual, mainly due
their extreme hairiness.
As you can see below, it is
only the whorl of sepals, called the calyx, that is hairy, but
leaflets that form a background to the bud. At this stage
sepals completely enclose the bud, and hide it from view.
In order to make the hairs on
sepals stand out more, I have used Photoshop’s ‘Levels’ function
increase contrast. This results in the false colour image
can be seen below.
A sequence of true colour
taken with increasing magnification follows. The bud
still hidden within the sepal cage.
A side view reveals that there
several overlapping rings of sepals forming the calyx.
As the bud swells, the
disk section becomes visible, with a colour mixture of green,
and light brown. Later, this central section appears a
All parts of this plant feel
to the touch. The reason is obvious! Fine, dense
every surface. Near the growing tips of stalks and stems,
surfaces are a uniform green colour.
Lower sections of the plant’s
and stalks possess red accents.
Near the base of the plant,
number and size of these red areas increases. Notice that
main stem of the plant has longitudinal grooves and ridges on
surface, while the branching stalks have an almost perfectly
Three closer views of these
stems can be seen below. The density of hairs on the
appears greater than in the grooves.
Here are two views showing the
surface, and edge of a leaf. It’s no wonder that leaves
to the touch!
Photomicrographs of the hairs
that they are segmented, and have spots on their surfaces.
Higher magnifications show
spots more clearly.
The point of connection of a
to the edge of the leaf is an amazingly complex structure with
various shapes and sizes contributing to the engineering.
Hairs shown in the previous
were growing from the edge of a leaf. The ones shown below
from the veins on the underside of a leaf.
Blooming Black-Eyed Susan
possess a central purple disk, a surrounding yellowish-green
finally, a ragged perimeter containing pointed ray petals.
Members of the Asteraceae family have composite
Although what you see in the images that follow appear to be
flowers, this is not correct. Each flower-head contains
central, small disk flowers, and an outer ring of larger ray
The central purple disk is not
composed of disk flowers at this point. They are too short
this early stage to stick up beyond the purple, hair-like
(These structures will be examined in more detail later in the
Views of a flower-head from
different angles show the ray-flower petals. They too feel
to the touch. What is the reason for this phenomenon?
It should not be a surprise to
that these too are covered with masses of fine hairs.
Hairs grow along the edge of
They also grow from both the
and lower surfaces of petals.
In order to increase the
and thus provide a clearer view of these hairs, I used
‘Levels’ function. This accounts for the false-colours in
following images. In the first and last images, I suspect
the roughly spherical purplish-brown objects are pollen grains.
Although the circular mat of
purplish-brown hairs at a flower-head’s centre appears
looks can be deceiving. The hairs surround each of the
flowers, and as the disk flowers grow longer, they eventually
taller than the hairs and hide them from view. In the
of the images below, there are hairs between the nearby green
flower buds, but they are too short to be visible.
of the Asteraceae family usually have a pappus associated with
individual ray and disk floret which surrounds the base of the
(corolla). The pappus may look like tiny hairs, as in this
species, or like teeth or scales. The name is derived from
Latin pappus which
a (whiskery) old man.
If many ray and disk florets
removed from the flower-head, these reddish pappi, (plural of
are clearly visible surrounding each floret.
The pappi surrounding the
florets appear to be smaller than those associated with disk
florets. Notice the tiny sucking insect in the third
Closer views of the insect can
More highly magnified views of
Under the microscope, more
of these pappi are revealed. The dark-ground illumination
shows clearly their intense red colour.
Surprisingly, at the point
the pappi are joined to the disk floret, there are stomata
guard cells that are usually associated with the underside of
leaves. (These control gas entry and egress into and out
For comparison, here are
images showing the appearance of pappi in a bud-stage
The hair-like structures
with a pappus in the immature flower-head are generally shorter
those in a mature pappus.
Cellular structure details in
lower segment of a pappus can be seen in the image below.
I have chosen not to include a
study of the reproductive structures in this plant because many
other articles on other members of the Aster family have already
covered the topic.
The low magnification, (to
macro-photographs were taken using a 13 megapixel Canon 5D full
DSLR, using a Canon EF 180 mm 1:3.5 L Macro lens.
A 10 megapixel Canon 40D DSLR,
equipped with a specialized high magnification (1x to 5x) Canon
lens, the MP-E 65 mm 1:2.8, was used to take the remainder of
The photomicrographs were
using a Leitz SM-Pol microscope (using a dark ground condenser),
the Coolpix 4500.
A Flower Garden of
A complete graphical index of
of my flower articles can be found here.
The Colourful World
A complete graphical index of
of my crystal articles can be found here.
Microscopy UK or their contributors.
Published in the
November 2012 edition of Micscape.
Please report any Web
offer general comments to the Micscape
Micscape is the on-line monthly
of the Microscopy UK web
site at Microscopy-UK
Onview.net Ltd, Microscopy-UK, and all contributors 1995
rights reserved. Main site is at www.microscopy-uk.org.uk
with full mirror at www.microscopy-uk.net .